Instabilities in parity-time symmetric non-Kerr fiber Bragg gratings

We study the phenomenon of modulational instabilities (MI) in a parity-time (PT)-symmetric fiber Bragg grating (FBGs) by considering the higher order nonlinearities. In the present investigation, we pinpoint different roles of gain/loss parameter on modulation instability gain spectra at various PT-symmetry breaking points, including unbroken, singularity and broken PT-symmetric regimes. Prior to the analysis of MI dynamics, we also present a detailed analysis of nonlinear dispersion curves and identify the ramifications of both cubic and quintic nonlinearities. Such a crucial investigation will find implications corresponding to the formation and dynamics of gap solitons in the so-called PT-symmetric media.